Many existing and future mobile vehicular applications require high data rate broadcasting systems ensuring full continental coverage. With respect to terrestrial networks, satellite broadcasting allows having continuous and trans-national coverage of a continent, including rural areas. Among existing satellite systems, Ku-band capacity is widely available in Europe, North America and most of the other regions in the world and can easily handle, at a low cost, fast and high-capacity communications services for commercial, military and entertainment applications.
The application of Ku-band to mobile terminals typically requires the use of automatic tracking antennas that are able to steer the beam in azimuth, elevation and polarization to follow the satellite position while the vehicle is in motion. Moreover, the antenna should be “low-profile”, small and lightweight, thereby fulfilling the stringent aerodynamic and mass constraints encountered in the typical mounting of antennas in airborne and automotive environments.
Typical approaches for beam steering are full mechanical scan or full electronic scan. The main disadvantages of the first approach for mobile terminals is the bulkiness of the structure due to the size and weight of mechanical parts, the reduced reliability because mechanical moving parts are more subject to wear and tear than electronic components, and high assembling costs making the approach less suitable for mass production. In comparison, the main drawback of fully electronic steering is that the antenna requires the integration of a lot of expensive analog RF electronic components which may prohibitively raise the cost for commercial applications.
An advantageous approach is to use a “hybrid” steerable beam antenna implementing a mechanical rotation in azimuth and electronic scanning in elevation. This approach requires only a simple single axis mechanical rotation and a reduced number of electronic components. These characteristics allow for maintaining a low production cost due to reduced mechanical parts and electronic components, reducing the size and the “height” of the antenna which is important in airborne and automotive applications, and having a better reliability factor than a fully mechanical approach due to fewer mechanical parts.
The ideal requirement for steerable beam antennas is to be capable of orientating the beam in any direction while maintaining a similar level of performance in all directions. This is possible only with mechanically steerable antennas having the freedom to rotate in any direction.
The performances of low-profile planar antennas mounted on a horizontal surface are typically decreased at low elevation angles due to a size reduction of the equivalent surface projected in the direction of the satellite. The use of antenna arrays with a hybrid steering mechanism (azimuth rotation) allows optimization of the radiating element pattern in a preferred direction.
Another advantageous antenna configuration is achieved by inclining the radiating elements in order to better focus the radiated power toward low elevation angles. Shaping of the radiation pattern does not allow an increase in the absolute level of the antenna performances, which has a maximum limit imposed by the equivalent surface, but it does allow a reduction in the number of elements in the array and hence reduces the number of electronic components required to electronically steer the beam in elevation.
However, the use of inclined radiating elements has generally important limitations on the radiation at low elevation due to the blockage of the field of view for the elements behind the first row. Thus, there is a need for a system and method for increasing the efficiency of an antenna at low elevation scanning.